We have found the enzyme, GTP cyclohydrolase, in extracts of the fruit fly, Drosophila melanogaster, and have evidence that this enzyme catalyzes the production of dihydroneopterin triphosphate. The latter compound is assumed to be an intermediate in the biosynthesis of all of the pteridines known to occur in the fruit fly. We have some preliminary evidence for the enzymatic conversion of dihydroneopterin triphosphate to the following pteridine products: sepiapterin, pterin, biopterin and drosopterin. We plan to investigate each of these enzyme systems individually to elucidate the biosynthetic pathways for these transformations and to understand the individual enzymatic reactions involved in the conversions. We plan to continue our efforts to understand the enzyme systems responsible for the production of Beta-alanine both in bacterial and animal systems. In particular, we shall concentrate on the identification of the prosthetic group associated with the bacterial enzyme that catalyzes the decarboxylation of aspartic acid to produce B-alanine. BIBLIOGRAPHIC REFERENCES: C.L. Fan and G.M. Brown, The Partial Purification and Properties of Guanosine Triphosphate Cyclohydrolase from Drosophila melanogaster. Biochem. Genetics, 14, 259 (1976). C.L. Fan, L. M. Hall, A.J. Skrinska and G.M. Brown, Correlation of Guanosine Triphosphate Cyclohydrolase Activity and the Synthesis of Pterins in Drosophila melanogaster. Biochem. Genetics, 14, 271 (1976).